Main menu

The Recycling Process

Paper recycling is a large scale, multi-step process with the objective to recover the paper fibers, and often other paper components such as mineral fillers, and use them as a raw material to produce new paper. Depending on the types of paper sourced for recycling and the final application, each recycling system is optimized accordingly. Typically kraft papers, corrugated board and packaging board are segregated from graphical papers at the collection and sorting step. Almost all papers can be recovered and, with the proper processing, be used to produce new paper. The importance of paper recycling and deinking can be seen in The European Declaration on Paper Recycling where it stated “Close attention is also being paid to improving the recyclability and – where applicable – the deinkability of paper-based products.”

Deinking of Paper

Many types of paper are subject to a deinking step in order to remove ink from the paper in preparation for producing new paper. Depending on the type of incoming paper and the requirements of the end product, various types of deinking technologies can be utilized. The most common types of deinking are the following:

Flotation Deinking

Process – In flotation deinking ink is removed through addition of chemicals such as surfactants and subsequent air introduction into the recovered pulp. The hydrophobic components such as ink particles are then selectively flotated and these components are then removed in the resulting foam.

Application – Flotation deinking is the most widely used method for ink removal in the deinking of graphic papers such as newsprint and magazine papers and also commonly used as one of the steps for deinking of papers for the production of hygiene papers. Flotation deinking is increasingly being used for producing recovered pulp for the white layers in recycled carton board and white-top corrugated liner.

Bleaching

Process – Bleaching, is the destruction of colorants in inks and the brightening of the pulp using bleaching agents such as hydrogen peroxide and sodium dithionite added during the pulping step and/or in a separate bleaching step.

Application – Bleaching is typically used to brighten recovered pulp for the production of higher quality graphic papers such as improved newsprint, for other high brightness recycled printing papers and for hygiene papers.

Washing

Process – Washing is the removal of inks and other unwanted components in the recovered pulp such as mineral fillers by washing the pulp in a diluted form on a wire screen. The fibers are recovered on the screen and the filtrate is treated to remove the unwanted solid material. Washing is only effective in the removal of small particle size inks.

Application – Washing is commonly used in the production of hygiene papers since the mineral fillers in the paper for recycling often lead to a reduction in the quality of the hygiene products and are therefore desired to be removed. Washing is also sometimes used as an additional step for producing high quality recovered market pulps from office papers. Washing is typically not used for the production of graphic papers due to the high yield loss in this process.

Most graphic paper recyclers today utilize a two loop flotation deinking system. Additionally, optional bleaching process capability with oxidative (peroxide) and sometimes reductive (dithionite) steps is often installed in these processes to enable the production of higher brightness paper grades such as improved newsprint, or, in undesirable cases, to compensate for decreased quality of the paper for recycling. These deinking systems are generally very robust to allow the utilization of printed papers from many sources. The common design options for state of the art graphic paper deinking are shown below (image courtesy of INGEDE).

An example of a recently installed, modern graphic paper deinking process is shown below (image courtesy of Voith Paper).

Flotation Deinking

In a flotation deinking plant, most ink removal occurs in the flotation process step. Most of the ink particles have already detached from the fibers prior to this stage. Flotation uses small bubbles that raise the inks to the surface in a froth which is then skimmed away. The remaining pulp fibers are then sometimes bleached to raise their brightness levels. Depending on the deinked pulp specifications, a second flotation loop is used for additional ink removal. Because of the variety of papers collected, and the mix of grades used as source papers, automated process control is often used to constantly monitor and adjust the quality of the deinked pulp.

A common test to assess deinkability is INGEDE Method 11, combined with the European Recovered Paper Council (ERPC) Scorecard. INGEDE Method 11 is a lab test that measures ink removal efficiency of a single flotation cell on a specific ink-paper combination. It was primarily designed to test the suitability of graphic papers for flotation deinking, for example of newsprint and magazines. It is a good test for assessing the single loop flotation removal using alkaline pulping and flotation conditions, without washing or bleaching stages. Its use today has been expanded to assess other ink and paper combinations and can typically be used to predict the degree that a given ink floats away from paper fibers at a nominal lab condition.

For this reason, it is a good screening test to estimate certain parameters relating to flotation deinking such as degree of ink removal from fibers and tendency of ink to accumulate in process water circulation systems. It should be noted that this method does not give an absolute measure of deinkability for all types of deinking plants, however according to INGEDE, a positive test result is the minimum requirement to be fulfilled, when assessing a paper-ink combination for suitability in a process utilizing only flotation deinking.

For many recycled paper qualities, a much more stringent requirement on the deinkability is necessary to attain the target properties. The deinkability requirements for the paper for recycling concerning optical properties is dependant on the target paper properties and the process capabilities of the deinking plant.